The disclosed invention relates to time compression correlation of signals that very with time. Particularly, the disclosed invention is directed to a delay line correlation circuit commonly referred to by the acronym DELTIC (Delay Line Time Compressor) for use in a sonar system.
Time compression correlation circuits are generally known in the art, and examples of such prior art are in U.S. Pat. No. 3,354,297, issued Nov. 21, 1967 to G.W. Anderson et al, and U.S. Pat. No. 3,449,553, issued on June 10, 1969. The application of time compression correlation circuits in sonar system is discussed in Allen and Westerfield, Digital Compressed--Time Correlators and Matched Filters for Active Sonar, The Journal of the Acoustical Society of America, Vol. 36, No. 1, page 121 (January 1964).
Also known in the art is the application of time compression correlation circuits in sonar systems for beam forming. See, for example, Allen and Westerfield, referenced above, at page 122. Briefly, beam forming involves the correlation of two sets of variable data wherein each set is representative of the output of a corresponding hydrophone. Such correlation can be performed by a DELTIC. Each respective set of variable data is in correct time sequence, but the respective sets of data will be selectively time displaced with respect to each other. Since the spacing of the hydrophones is known, a particular time displacement represents pressure waves from a particular direction. That particular direction can be referred to as a beam angle. Thus, the hydrophone pair can be considered as looking at a given direction as a function of time displacement. Obviously, for zero time displacement, the direction being examined is perpendicular to the line segment drawn between hydrophones. Time displacement will result in a beam angle with respect to such perpendicular direction.
Prior art time compression correlators, however, have several disadvantages. For example, the system of U.S. Pat. No. 3,354,297 utilizes a complicated electromechanical magnetic storage drum. The system of U.S. Pat. No. 3,449,553 is complex and requires a large number of components. Still other systems require high clocking frequencies or critical timing. In some systems, race paths are utilized which could result in lost or erroneous data, thereby reducing the reliability of such race path systems. Another disadvantage of prior art systems is excessive power dissipation, often resulting from high frequency timing requirements.
Therefore, it is an object of the subject invention to provide an improved delay line time compression correlation circuit which uses the minimum clock frequency necessary for performing the correlation functions.
Another object of the disclosed invention is to provide an improved delay line time compression correlation circuit which does not use race paths and has increased reliability.
A further object of the subject invention is to provide an improved delay line time compression correlation circuit with low power dissipation.